1. Field of the Invention
The present invention relates to an absorbent article such as a disposable diaper, a sanitary napkin, a pantie liner or a urine absorbing pad and, more particularly, to an absorbent article using a back sheet having regions, which are different in the degree of orientation, and a method for manufacturing the back sheet.
2. Related Art
In order to absorb discharges, there have been recently employed a number of absorbent articles such as disposable diapers, sanitary napkins, pantie liners or urine absorbing pads. When a discharge is made while the absorbent article is worn, the absorbent article having absorbed the discharge is disposed of and is replaced by a new one.
Here, the back sheet to be ordinarily employed in the absorbent article is exemplified by a liquid-impermeable resin sheet. The back sheet is formed by stretching a resin film containing an inorganic filler so as to enhance the air-permeability and the moisture-permeability so that the back sheet is made opaque. In the case of the diaper, therefore, in order to confirm whether or not the wearer has made a discharge, the care taker has to remove the diaper from the wearer to confirm the inside of the diaper. This is a seriously troublesome work for the care taker.
In Unexamined Published Japanese Patent Application No. 5-168660, therefore, there is disclosed a uniaxially oriented air-permeable film which is embossed to have a moisture-permeability of 1,000 g/m2/24 hrs or more so as to enhance the optical transmittance. In this film, however, the moisture-permeability is not so lowered that the optical transmittance cannot be enhanced so high.
In unexamined Published Japanese Patent Application No. 10-85257, on the other hand, there is disclosed a back sheet of a developing type disposable diaper. In this back sheet, a see-through portion is formed in at least a central portion in the longitudinal direction. This back sheet is formed like before of a porous sheet, which is prepared by stretching the resin film containing the inorganic filler, for enhancing the moisture-permeability. In the see-through portion, a transparent portion is formed by crushing the pores of the porous sheet by an embossing treatment thereby to eliminate the scattering of light. If the porous sheet is further embossed, however, pin holes will be easily formed, because the embossed portion is lowered in its strength. There is also a description that the transparent portion could be formed by applying wax, varnish or hot melt in place of the embossing treatment. However, the applied material will ooze or stick on the film surface and requires a drying treatment after applied, so that the cost for the material and for the treatment rises.
Thus in the disposable diaper, there has been demanded a back sheet which is so enhanced in the optical transmittance that whether or not the discharge has been made can be confirmed from the outside without lowering the air-permeability, the moisture-permeability or the strength.
Here will be described a sanitary napkin. This sanitary napkin may be provided on the two longitudinally extending sides with wings which extend in the width direction. When the sanitary napkin is worn, the wings are folded back to the lower side of the crotch portion of the underwear such as panties so that the edge portions of the panties can be prevented from being blotted with the discharge. Moreover, the napkin can be prevented from going out of position by adhesion means disposed on the wings for attaching the napkin to the panties. These wings are formed by protruding the member constructing the body of the napkin, such as the adhered back sheet and top sheet, in the width direction from the two side portions of the body of the napkin.
In the back sheet of the sanitary napkin, however, the back sheet is formed as in the diaper by stretching the film so as to enhance the air-permeability so that the optical transmittance is extremely lowered. When the panties wearing the napkin with the wings is seen from the outside, therefore, the presence of the wing portions, i.e., the wearing of the napkin is apparent from the outside. Only the wings could be made of a material different from that of the back sheet, such as a high optical transmittance sheet so that the wearing of the napkin could not be confirmed in the appearance. However, this makes the manufacture process complex to raise the cost.
Thus, the absorbent article has been desired to have a partially high optical transmittance. However, the portion desired to have a high optical transmittance is different among the kinds of absorbent articles.
An object of the invention is to provide an absorbent article using a back sheet which has a high optical transmittance portion and an air- and moisture-permeable portion.
Another object of the invention is to provide a method for manufacturing the back sheet.
According to an aspect of the invention, there is provided an absorbent article comprising: a liquid-permeable top sheet; a back sheet; and an absorbent core sandwiched between the top sheet and back sheet, wherein the back sheet is formed of a resin film containing an inorganic filler in a resin base material, and wherein the back sheet includes: (a) a stretched moisture-permeable region; and (b) a high optical transmittance region having a lower degree of orientation than that of the moisture-permeable region and/or left unstretched.
In the absorbent article of the invention, there are formed in one back sheet the high optical transmittance region and the high air- and moisture-permeable region. As a result, the high optical transmittance region can be formed in a portion of the absorbent article while the air-permeability and the moisture-permeability being retained in the entire absorbent article. In the diaper, for example, whether or not the discharge has been made can be confirmed from the outside of the diaper being worn. In the sanitary napkin, the presence of the wings cannot be seen from the outside of the panties. Moreover, this strength of the back sheet is hard to degrade.
The resin base material is preferably a polyolefin resin.
The mixing ratio between the resin base material and the inorganic filler is preferably 20 to 70% by mass:80 to 30% by mass.
In the case where the absorbent article is a disposable diaper, the high optical transmittance region (b) is preferably positioned to cover the entirety or a portion of the back of the absorbent core. In this case, furthermore, the high optical transmittance region (b) is preferably provided in the generally widthwise central portion of the region having the absorbent core and in the region containing the widthwise center of the absorbent core and having one quarter of the width size of the diaper, and/or in the generally longitudinal central portion of the region having the absorbent core and in the region containing the longitudinal center of the absorbent core and having one quarter of the longitudinal size of the diaper.
It should be noted that: the term xe2x80x9clongitudinal central portion/regionxe2x80x9d as used herein means the intermediate portion/region located between two end regions lying opposite one another in the longitudinal direction; the term xe2x80x9cwidthwise central portion/regionxe2x80x9d as used herein means the intermediate portion/region located between two side regions lying opposite one another in the widthwise direction. It should be also noted that: the term xe2x80x9clongitudinal centerxe2x80x9d as used herein means the midpoint located between two end edges lying opposite one another in the longitudinal direction; the term xe2x80x9cwidthwise centerxe2x80x9d as used herein means the midpoint located between two side edges lying opposite one another in the widthwise direction.
In the case where the absorbent article is a sanitary napkin including a pair of wing portions disposed on the two sides of the region of the absorbent core and extending outwardly in the widthwise direction, on the other hand, the moisture-permeable region (a) is preferably positioned to cover the entirety or a portion of the back of the absorbent core whereas the high optical transmittance region (b) is preferably positioned in at least the wing portions. In this case, furthermore, the moisture-permeable region (a) is preferably positioned in the generally widthwise central portion of the region having the absorbent core and over one half or more of the width size of the absorbent core, and/or in the generally longitudinal central portion of the region having the absorbent core and over one half or more of the longitudinal size of the absorbent core.
The moisture-permeable region (a) is preferred to have a moisture-permeability of 1,000 g/m2xc2x724 hrs or more.
The moisture-permeable region (a) is preferred to have a total optical transmittance of 50% or less according to JIS-K-7105.
The high optical transmittance region (b) is preferred to have a total optical transmittance of 60% or more according to JIS-K-7105.
If the back sheet in the moisture-permeable regions (a) has a thickness T1 and if the back sheet in the high optical transmittance region (b) has a thickness T2, it is preferred that the values T1 and T2 satisfy the following Formulas:
20xe2x89xa6{(T2xe2x88x92T1)/T1}xc3x97100xe2x89xa630.
The back sheet may have a multi-layered structure in at least the high optical transmittance region (b).
The back sheet to be used in the absorbent article of the invention can be formed simply at a low cost. According to another aspect of the invention, there is provided a method for manufacturing a back sheet for an absorbent article including: a liquid-permeable top sheet; the back sheet; and an absorbent core sandwiched between the top sheet and back sheet. A film containing an inorganic filler in a resin base material is partially stretched to form: (a) a stretched moisture-permeable region; and (b) a high optical transmittance region having a lower degree of orientation than that of the moisture-permeable region and/or left unstretched.
In the above, a film being continuously fed may be stretched exclusively at a central portion in a width direction (or in CD) thereof to form the moisture-permeable region (a) at the central portion.
In an alternative, a film being continuously fed may be stretched exclusively on two side portions in a width direction (or in CD) thereof to form the moisture-permeable regions (a) on the two side portions.
In another alternative, a film being continuously fed may be partially stretched at a predetermined interval in a longitudinal direction (or in MD) thereof to form the moisture-permeable regions (a) at a spacing in the longitudinal direction.
In still another alternative, a film being continuously fed may be partially stretched at a predetermined interval in a width direction (or in CD) thereof to form the moisture-permeable regions (a) at a spacing in the width direction.
The film may be stretched by an embossing treatment to form the moisture-permeable region (a).
It is possible that a film having partially different thicknesses is formed of a material containing the inorganic filler in the resin base material and is stretched to form the moisture-permeable region (a) in the thinner portion and the high optical transmittance region (b) in the thicker portion.
It is also possible that an unstretched film is partially coated with a transparent film and is then stretched to form the moisture-permeable region (a) in the portion, which is not coated with the transparent film, and the high optical transmittance region (b) in the portion which is coated with the transparent film.